One newly hatched chick looks much like another: even their parents can't tell them apart. But as Steve Insley explains, that isn't necessary for many species; they only need to begin recognising their chicks once there is a chance that the youngsters might get mixed up with someone else's brood. Until then it's good enough to find the right nest. But once the youngsters take to their wings, it's a different story, and this is the point when many parents begin to distinguish their chicks from the youngsters next door. But not all parents take equal responsibility for their recently fledged chicks. When young razorbills leave the nest, it's not mum, but dad, who takes them out on their first foraging trips at sea. Insley wondered if this might affect which parent could recognise their young. Could there be sex-related differences in the parent's ability to recognise their own young? Insley set out to the windswept Gannet Islands off the North American Labrador coast to see if there was a difference between male and female razorbill's ability to recognise their own young. After weeks of patiently watching adult razorbill's reactions to fledged chick's voices, Insley was amazed to discover that there is a sex bias in the bird's ability to recognise their own chicks' voices; fathers responded enthusiastically but mothers did not (p. 25).

Insley teamed up with Rosana Paredes and Ian Jones, who were already working on the islands with the birds. First Insley and Paredes had to work out how to uniquely identify each adult bird by using hair dye without `spooking' the birds. Only then could Insley begin recording the cries of both the chicks and adults. But even on a clear day, the elements conspired to disrupt the recordings with the recordings picking up high levels of background noise from the wind and the sea.

Once Insley had a satisfactory set of bird-call recordings from adults and chicks, he began testing whether the birds responded to each other. First he played the cries of nearly fledged chicks to their parents and strangers. He recorded the adult bird's responses to the recordings. He explains that the adults reacted in several ways when they heard their chicks, but the most reliable indicator that the adult had recognised a chick was that the adult called back. Insley was elated when he realised that fathers mainly responded to their own chicks, usually remaining silent when they heard an unrelated chick, but the mothers were indifferent to all of the chick's recordings, whether or not they were related.

Were the females ignoring the chicks, or were they unable to respond to the recorded bird's cries? Insley knew that the parents often duetted together when they returned to the nest, so he tried playing the females the sounds of their partners' voice. This time the females showed more interest, and responded to the male's sounds. So the females could respond to a recorded sound that they recognise, but there could be several other reasons why they don't respond to their own chicks.

Having found that there is a link between the males' behaviour and their ability to recognise their young, Insley is keen to see what impact this has on the razorbill's paternalistic society.

Insley, S. J., Paredes, R. and Jones, I. L. (
). Sex differences in razorbill Alca torda parent—offspring vocal recognition.
J. Exp. Biol.